The invention concerns the field of optical components and more particularly optical wavelength multiplexers and demultiplexers.
The person skilled in the art knows that it is possible to considerably increase the traffic of fiber optic networks through wavelength multiplexing and demultiplexing techniques. Each series of data to be transported is transmitted over a specific optical frequency, multiplying the capacity of the fiber by the number of wavelengths used.
FIG. 1 represents a multiplexer of the prior art. In this type of multiplexer, basic optical fibers 1 to 4 each dedicated to a frequency band have their end in a plane x constituting the input plane of the multiplexer. This multiplexer also comprises a collimation element 6 and a diffractive element 7. The input plane x of the multiplexer is confused with the focal plane of the collimation element 6 so that the input beams coming from the ends of the basic fibers 1 to 4 pass through the collimation element 6 and are located roughly parallel to one another. The diffraction element 7 is positioned so that the beams are sent back toward the collimation element 6, which superimposes them to introduce them at the end of a single output fiber 5.
As the rate of optical networks continues to increase and as the stability of the optical sources, particularly lasers, is not perfect, it is necessary to reduce the transmission fluctuations resulting from this instability by seeking a multiplexing bandwidth that is as wide as possible.
We therefore want to increase the ratio FWHM/Δλ where FWHM (Full Width at Half Maximum) designates the width of a basic band and Δλ designates the distance between two central wavelengths of two consecutive basic bands. We know that the ratio FWHM/Δλ is proportional to the ratio ω/Δλ, where ω designates the mode field radius of the fibers and Δx designates the spacing between the fibers.